Method and device for producing water for pure water, and method and system for producing pure water

Abstract

Provided are a method and a device for producing water for pure water, with which it is possible to efficiently add a chemical to water supplied to a reverse osmosis membrane when raw water containing chlorine is subjected to a reverse osmosis membrane treatment. A method for producing water for pure water, the method comprising: a step for obtaining first treated water by adding polyaluminum chloride to raw water containing free chlorine; a step in which a reducing agent having sodium pyrosulfite as an active ingredient is added to the first treated water to obtain second treated water; and a reverse osmosis membrane step in which the second treated water is subjected to a reverse osmosis membrane treatment.

Description

Technical Field

[0001] The present invention relates to a method and device for producing pure water, a method for producing pure water, and a system for producing pure water. Background Art

[0002] In water treatment such as the manufacture of industrial water and wastewater treatment from river water, well water, lake water, etc., coagulation treatment is performed to remove suspended matter such as suspended matter, dissolved organic matter, colloidal silica, etc. In this coagulation treatment, polyaluminium chloride (PAC) is used as a coagulant. PAC has become popular because of its low cost and wide pH range for coagulation.

[0003] As a method for using PAC in the production of industrial water and wastewater treatment, the following method is known: PAC with a low alkalinity (less than 75%) is mixed into wastewater to form coarse aggregates of suspended matter, and the coarse aggregates are removed by dead-end filtration (for example, refer to Patent Document 1). However, this method requires a slow-rate filtration device, and therefore requires a large area for installing the slow-rate filtration device. For example, assuming that 100 m 3 / When treating raw water of h, a circular slow-speed filtration device with a radius of 12m is required. In addition, there is no equipment for further treatment of treated water, and it is difficult to apply it except for extremely limited equipment such as water purification plants. Therefore, it is difficult to apply it to the production of pure water and ultrapure water.

[0004] Therefore, a microfloc method using PAC is also used. This method is a method in which PAC is directly injected into tap water, industrial tap water, etc., or rapidly stirred after injection to form microflocs, which are then removed by filtration without sedimentation (for example, see Patent Document 2).

[0005] In the production of pure water and ultrapure water used in the manufacturing processes of semiconductors, liquid crystals, etc., tap water, industrial tap water, etc. are used as raw water. The pre-treated raw water is passed through a membrane treatment device such as a reverse osmosis membrane device (RO) and an ultrafiltration device (UF), and then treated with a combination of an ion exchange resin device, an ultraviolet irradiation device, etc.

[0006] Here, in order to prevent the proliferation of live bacteria present in the raw water in the above-mentioned pretreatment, and to prevent the generation of problems such as slime, the treatment is usually carried out on the basis of adding chlorine-based bactericides such as hypochlorous acid. However, if the raw water containing free chlorine (also called residual chlorine) derived from the bactericide is subjected to reverse osmosis membrane treatment, the reverse osmosis membrane will be rapidly deteriorated, so before being supplied to the reverse osmosis membrane device, a process of decomposing the free chlorine using a reducing agent is carried out. Moreover, in order to prevent the problems caused by live bacteria in the latter section, after adding the reducing agent, a process of adding an oxidizing bactericide other than the free chlorine system is carried out. However, in this method, an excessive amount of reducing agent is added in order to completely decompose the free chlorine, so a surplus of reducing agent is generated, and thus the oxidizing bactericide is decomposed and disappears. The decomposition and disappearance of the oxidizing bactericide easily leads to a biofilm caused by live bacteria, so a process of excessively adding an oxidizing bactericide corresponding to the surplus amount of the reducing agent is also carried out. However, in these methods, there are the following problems: the control of the amount of reducing agent and oxidizing agent added is complicated; the amount of reducing agent and oxidizing agent added becomes more. To address this problem, there is known an apparatus that provides a unit for measuring the residual chlorine concentration in raw water and controls the injection of a reducing agent by an injection unit so that a predetermined chlorine concentration remains (for example, see Patent Document 3). In addition, attempts have been made to use a mixture of a chlorine-based fungicide and an aminosulfonic acid compound instead of a chlorine-based fungicide to sterilize live bacteria in raw water. However, in raw water containing a large amount of live bacteria, the amount of chlorine-based fungicide and aminosulfonic acid compound added increases, resulting in a problem that a trace amount of free chlorine contained in the mixture of the chlorine-based fungicide and aminosulfonic acid compound remains in the raw water (for example, see Patent Document 4). Prior art literature Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2012-086149 Patent Document 2: Japanese Patent Application Publication No. 2022-165279 Patent Document 3: Japanese Patent Application Publication No. 2021-137710 Patent Document 4: Japanese Patent Application Publication No. 2010-202524 Summary of the invention

[0008] As described above, in the production of pure water and ultrapure water, when raw water containing residual chlorine is subjected to reverse osmosis membrane treatment, there are problems such as complicated control of the amount of oxidant and reductant added and increased amount of chemicals used. The increased amount of chemicals used will lead to increased costs and environmental load. Furthermore, it is difficult to quantify the excess amount of reducing agent added, and therefore it is also difficult to set the optimal amount of the agent used.

[0009] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method and apparatus for producing pure water, which can efficiently add a chemical to water supplied to a reverse osmosis membrane. Another object of the present invention is to provide a pure water production method and production system capable of efficiently adding a chemical to water supplied to a reverse osmosis membrane.

[0010] The production method, production apparatus, and pure water production system according to the embodiments of the present invention are as follows. [1] A method for producing pure water, comprising: a step of adding polyaluminium chloride to raw water containing free chlorine to obtain first treated water; a step of adding a reducing agent containing sodium pyrosulfite as an active ingredient to the first treated water to obtain second treated water; and a reverse osmosis membrane step of subjecting the second treated water to reverse osmosis membrane treatment. [2] The production method according to [1], wherein high-basicity polyaluminium chloride is added to the raw water to obtain first treated water containing microflocs. [3] The production method according to [1] or [2], wherein the turbidity of the raw water is greater than or equal to 1 NTU and less than or equal to 100 NTU. [4] The production method according to any one of [1] to [3], wherein the basicity of the polyaluminium chloride is greater than 75%. [5] The production method according to any one of [1] to [4], wherein the polyaluminum chloride contains hydroxyaluminum chloride, and the amount of hydroxyaluminum chloride added is 0.25 mg / L or more and 5 mg / L or less relative to the raw water, calculated as the concentration of aluminum oxide (Al2O3).

[0011] [6] The manufacturing method according to [1] to [5] includes: a filtration step, filtering the first treated water through one or more selected from sand filtration, multi-media filter (MMF) filtration, microfiltration (MF) device and ultrafiltration, and adding the reducing agent to the treated water obtained in the filtration step. [7] The production method according to [1] to [6], wherein the free chlorine concentration in the raw water is 0.1 mg / L or more and 2 mg / L or less in terms of Cl2, and the amount of the reducing agent added is 0.1 mg / L or more and 5 mg / L or less in terms of sodium pyrosulfite. [8] The production method according to any one of [1] to [6], wherein the turbidity of the permeate water of the reverse osmosis membrane device is greater than or equal to 0.01 and less than or equal to 0.4, and the aluminum concentration is greater than or equal to 0.01 mg / L and less than or equal to 0.04 mg / L.

[0012] [9] A method for producing pure water, comprising: a process for producing pure water, including: a process for adding polyaluminium chloride to raw water containing free chlorine to obtain first treated water; a process for adding a reducing agent containing sodium pyrosulfite as an effective ingredient to the first treated water to obtain second treated water; a reverse osmosis membrane process for treating the second treated water with a reverse osmosis membrane; an ultraviolet oxidation process; and an ion exchange process.

[0013]

[10] A device for producing pure water, comprising: a raw water supply device for supplying raw water containing free chlorine; a polyaluminium chloride supply device for adding polyaluminium chloride to the raw water; a reducing agent supply device for adding a reducing agent containing sodium pyrosulfite as an effective ingredient to first treated water generated by adding polyaluminium chloride to the raw water; and a reverse osmosis membrane device for performing reverse osmosis membrane treatment on second treated water generated by adding the reducing agent.

[11] The production apparatus according to

[10] , wherein the turbidity of the raw water is greater than or equal to 1 NTU and less than or equal to 100 NTU.

[12] The production apparatus according to

[10] or

[11] , wherein the basicity of the high-basicity polyaluminium chloride is greater than 75%.

[13] A manufacturing device according to any one of

[10] to

[12] , wherein the polyaluminum chloride contains hydroxyaluminum chloride, and the polyaluminum chloride supply device supplies hydroxyaluminum chloride in an amount of 0.25 mg / L to 5 mg / L relative to the raw water in terms of concentration converted to aluminum oxide (Al2O3).

[14] A manufacturing device according to any one of

[10] to

[13] , wherein between the polyaluminium chloride supply device and the reducing agent supply device, there is one or more selected from a sand filter device, a multi-media filter (MMF) filter device, a microfiltration (MF) device and an ultrafiltration device.

[15] A pure water production system comprising: a pure water production device as described in any one of

[10] to

[14] ; an ultraviolet oxidation device; and an ion exchange device. It should be noted that the symbol "to" indicates a numerical range including the numerical values ​​before and after it. In addition, all the added amounts are described based on the active ingredient.

[0014] According to the present invention, a method and an apparatus for producing pure water can be provided, which can efficiently add a chemical to water supplied to a reverse osmosis membrane. Furthermore, the present invention can provide a pure water production method and a production system which can produce high-quality pure water for a long period of time by efficiently adding a chemical to the water supplied to the reverse osmosis membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1This is a diagram schematically showing a production apparatus used in the method for producing pure water according to the embodiment. Figure 2 It is schematically represented in Figure 1 The manufacturing apparatus shown is also a diagram of a manufacturing apparatus having a mixing tank. Figure 3 This is a diagram schematically showing a production apparatus used in a method for producing pure water according to another embodiment. Figure 4 It is schematically represented in Figure 3 The manufacturing apparatus shown is also a diagram of a manufacturing apparatus having a mixing tank. Figure 5 It is a diagram schematically showing a pure water production system using the pure water production apparatus according to the embodiment. Figure 6 This is a diagram schematically showing a pure water production apparatus used in Examples. Figure 7 This is a graph showing the relationship between the raw water pH and the residual reducing agent amount in the experimental examples using sodium pyrosulfite, sodium sulfite, and sodium bisulfite. Description of Reference Numerals 1 to 4, 6: pure water production device; 5: ultrapure water production system; 11, 61: raw water supply device; 12, 62: polyaluminium chloride supply device; 13: raw water delivery pipe; 14, 64: reverse osmosis membrane device; 17, 67: reducing agent supply device; 18, 68: disinfectant supply device; 23, 63: mixing tank; 31: filter section; 65: ultrafiltration device; 50: pretreatment system; 51: primary pure water system (pure water production system); 52: secondary pure water system (subsystem); 53: point of use (POU); 513: ultraviolet oxidation device (TOC-UV); 514: ion exchange device; TK1, TK2: box; 521: ultraviolet oxidation device (TOC-UV); 522: non-regenerative ultrapure water production ion exchange device (Polisher); 523: membrane degassing device (MDG); 524: ultrafiltration device (UF). DETAILED DESCRIPTION

[0016] Hereinafter, embodiments of the present invention will be described. Figure 1The manufacturing device 1 used in the method for manufacturing pure water of the present embodiment is schematically shown. The manufacturing device 1 includes: a raw water supply device 11 for supplying raw water; a polyaluminum chloride supply device 12 for supplying polyaluminum chloride (hereinafter also referred to as "PAC"); a raw water delivery pipe 13 for delivering raw water; and a reverse osmosis membrane device 14 for performing reverse osmosis membrane treatment on raw water (first treated water) to which PAC is added. The manufacturing device 1 also includes: a reducing agent supply device 17 for adding a reducing agent to the supply water to the reverse osmosis membrane device 14; and a bactericide supply device 18 for adding an oxidizing bactericide to the supply water to which the reducing agent is added. A delivery pipe 15 for permeated water is connected to the permeation side of the reverse osmosis membrane device 14. A discharge pipe 16 for concentrated water is connected to the concentration side of the reverse osmosis membrane device 14. It should be noted that the bactericide supply device 18 is not essential and can be provided as needed.

[0017] The method for producing pure water for use using the embodiment of the manufacturing device 1 is as follows. First, raw water is supplied from the raw water supply device 11 to the raw water delivery pipe 13. Raw water is urban water such as municipal water and industrial water, or natural water such as river water, lake water, groundwater, and well water. The raw water contains free chlorine. Alternatively, free chlorine is sometimes added to the raw water during transportation using the raw water delivery pipe 13. As for the water quality of the raw water, for example, the turbidity is 1NTU to 100NTU, the suspended solids mass (SS) is 5mg / L to 500mg / L, the total organic carbon (TOC) is 0.5mg / L to 7mg / L, the aluminum concentration is 0.01mg / L to 5mg / L, the free chlorine concentration is 0.1mg / L to 2mg / L in terms of Cl2, and the pH is 4 to 9. The raw water supply device 11 includes, for example, a raw water tank for storing raw water and a water supply pump for conveying the raw water in the raw water tank, and the water supply pump supplies the raw water in the raw water tank to the raw water conveying pipe 13. It should be noted that in order to pre-treat the raw water before adding the high alkalinity PAC according to the water quality of the raw water, a pre-filter (not shown) may be installed as a pre-treatment device. In addition, an acid or alkali injection device for adjusting the pH of the raw water as needed may also be installed.

[0018] Next, the polyaluminium chloride supply device 12 adds PAC to the raw water delivery pipe 13. The polyaluminium chloride supply device 12 includes, for example, a chemical tank storing PAC and a chemical injection pump that adds PAC in the chemical tank to the raw water delivery pipe 13. The chemical injection pump measures PAC in the chemical tank to a predetermined concentration and adds it to the raw water delivery pipe 13. Thus, the first treated water is generated.

[0019] At this time, according to the alkalinity of PAC, the pH adjusting device (not shown) adds an acid and an alkali as pH adjusting agents to the raw water to adjust the pH of the raw water. The addition of the acid and the alkali may be either one or both. In the case of using a PAC with low alkalinity described later, the pH adjusting agent is added to the raw water delivery pipe 13 by the pH adjusting device to adjust the pH of the raw water before the addition of the PAC. The pH adjusting device, for example, includes an acid storage tank for storing acid and an acid injection pump for adding the acid in the acid storage tank to the raw water delivery pipe 13. In addition, the pH adjusting device includes an alkali storage tank for storing alkali and an alkali injection pump for adding the alkali in the alkali storage tank to the raw water delivery pipe 13. Then, the acid injection pump and the alkali injection pump measure the acid in the acid storage tank and the alkali in the alkali storage tank in such a way that the raw water becomes a specified pH, and add them to the raw water delivery pipe 13. The acid used here is typically sulfuric acid, and the alkali is typically sodium hydroxide (aqueous solution).

[0020] The PAC in the present embodiment includes polyaluminum chloride represented by the following chemical formula (1). As the PAC in the present embodiment, any of low-alkalinity PAC and high-alkalinity PAC can be used. As the PAC in the present embodiment, any of low-alkalinity PAC and high-alkalinity PAC is preferably used. When using low-alkalinity PAC (hereinafter referred to as "low-alkalinity PAC"), it is preferred to set the above-mentioned pH adjustment device to adjust the pH of the raw water. Alkalinity is a value calculated by n / 6×100(%). [Al2(OH) n Cl 6-n ] m (1≤n≤5, m≤10)……(1)

[0021] The basicity of low-basicity PAC is preferably 75% or less, more preferably 60% or more and 70% or less. Low-basicity PAC can be produced, for example, by the method described in Japanese Patent Publication No. 2009-203125. As low-basicity PAC, only one type can be used, or two or more types can be used in combination. When two or more types are used in combination, the basicity of the two or more low-basicity PACs may be the same or different, but the basicity of the low-basicity PACs used is preferably 75% or less, more preferably 60% or more and 70% or less.

[0022] The amount of low-alkalinity PAC is preferably 0.03 mg / L or more as Al2O3 relative to the turbidity 1NTU in the raw water. Specifically, the amount of low-alkalinity PAC is preferably 0.05 mg / L or more as Al2O3 and 5 mg / L or less as Al2O3 relative to the amount of raw water, and more preferably 0.1 mg / L or more as Al2O3 and 2 mg / L or less as Al2O3.

[0023] In the present embodiment, a high basicity PAC (hereinafter referred to as "high basicity PAC") is preferably used as the PAC. The basicity of the high basicity PAC is preferably greater than 75%, and more preferably greater than 83%. The upper limit of the basicity is usually less than about 84%. The high basicity PAC can be manufactured, for example, by the method described in Japanese Patent No. 4104773. As the high basicity PAC, only one type may be used, or two or more types may be used in combination. When two or more types are used in combination, the basicities of the two or more high basicity PACs may be the same or different, but the basicity of the high basicity PACs used is preferably greater than 75%, and more preferably greater than 83%.

[0024] When using high alkalinity PAC, suspended matter in the raw water interacts with high alkalinity PAC to form microflocs. By passing through the microflocs, the adhesion of residual aluminum to the membrane of the reverse osmosis membrane device 14 can be significantly reduced, and the performance of the reverse osmosis membrane device can be maintained for a long time. Microflocs are aggregates of suspended matter and high alkalinity PAC with a size of about 1 to 10 μm. High alkalinity PAC easily forms microflocs, but it is not easy to form coarse flocs larger than microflocs or flocs finer than microflocs (nanoflocs). Aluminum ions are not easy to leak out of microflocs, so by passing through the microflocs, the clogging of the reverse osmosis membrane can be prevented for a long time.

[0025] As a high basicity PAC, hydroxyaluminum chloride (Al2Cl(OH)5) is preferably used. Hydroxyaluminum chloride is a polyaluminum chloride in which n=5 and m=1 in the above chemical formula (1) and has a basicity of 83.3%. Hydroxyaluminum chloride is more likely to form more uniform microflocculates. This is believed to be due to the high basicity and small molecular weight of hydroxyaluminum chloride.

[0026] The amount of high basicity PAC is preferably 0.125 mg / L or more in terms of Al2O3 relative to the turbidity 1NTU in the raw water. Specifically, the amount of high basicity PAC is preferably 0.25 mg / L or more in terms of Al2O3 and 5 mg / L or less in terms of Al2O3 relative to the amount of raw water, and more preferably 0.3 mg / L or more in terms of Al2O3 and 3 mg / L or less in terms of Al2O3. In particular, when hydroxyaluminum chloride (Al2Cl(OH)5) is used as high basicity PAC, the amount of hydroxyaluminum chloride is preferably 0.25 mg / L or more in terms of Al2O3 and 2 mg / L or less in terms of Al2O3 relative to the total amount of raw water. Even if the amount of high basicity PAC is a small amount as described above, it is possible to microflocculate the suspended matter in the raw water. In addition, since high basicity PAC works even in a small amount as described above, it is easy to prevent clogging of the reverse osmosis membrane device 14 in the rear section. It should be noted that the expression "in terms of Al 2 O 3 " indicates a value converted into the concentration of aluminum oxide (Al 2 O 3 ).

[0027] Here, Figure 2 A pure water production device 2 having a mixing tank 23 for adding PAC to raw water is schematically shown. The production device 2 has a mixing tank 23 and a delivery pipe 131 for supplying treated water in the mixing tank 23 to a later stage on the path of the raw water delivery pipe 13, and is different from the above-mentioned production device 1 in that a reducing agent supply device 17 and a bactericide supply device 18 are connected on the path of the delivery pipe 131, but the other structures are the same. In this embodiment, detailed description of the same structure and function as the production method using the production device 1 is omitted.

[0028] In the production device 2, raw water is supplied from the raw water supply device 11 to the mixing tank 23, and PAC is supplied from the polyaluminium chloride supply device 12 to the mixing tank 23. When low alkalinity PAC is used, the pH adjustment device supplies acid and alkali to the mixing tank 23. Thus, first treated water is generated.

[0029] When using high-alkalinity PAC, since the pH dependence of the cohesion of high-alkalinity PAC is small, it is not necessary to add acid and alkali using a pH adjustment device. In addition, when using high-alkalinity PAC, suspended matter in raw water interacts with high-alkalinity PAC in the mixing tank 23, thereby forming microflocculates. The order of supplying to the mixing tank 23 may be either raw water or PAC first, or both. It is preferred to add PAC and acid and alkali added as needed to the mixing tank 23 supplied with raw water.

[0030] exist Figure 2 In the mixing tank 23 of the manufacturing device 2 shown, when using high-alkalinity PAC, by rapidly stirring the raw water and high-alkalinity PAC, nano-flocs are not generated, and more uniform micro-flocs are easily formed. The stirring speed is preferably 150s in terms of G value. -1 More than 150 s, more preferably 150 to 250 s -1 , more preferably 250s -1 In addition, the stirring time by the rapid stirring machine is 2 minutes or more, preferably 3 minutes or more, and more preferably 6 minutes or more. The greater the G value of the rapid stirring, the shorter the stirring time can be.

[0031] Next, the first treated water is supplied to Figure 1 The raw water delivery pipe 13 or Figure 2 In the process of the first treated water flowing in the raw water conveying pipe 13 (or the conveying pipe 131, hereinafter the same in this embodiment), the reducing agent supply device 17 adds the reducing agent to the first treated water. Thus, the second treated water is generated.

[0032] The reducing agent supply device 17 includes, for example, a chemical tank storing the reducing agent and an injection pump for adding the reducing agent in the chemical tank to the raw water pipe 13 . The injection pump measures a predetermined amount of the reducing agent in the chemical tank and adds the reducing agent to the raw water pipe 13 .

[0033] The reducing agent used in the manufacturing device 1 (or manufacturing device 2, which is the same in this embodiment below) of the present embodiment has sodium pyrosulfite (Na2S2O5) as an effective ingredient. The present inventors have found that when sodium pyrosulfite is used as a reducing agent, the amount of reducing agent remaining in the reaction with free chlorine is extremely small regardless of the pH value of the raw water. Therefore, the amount of oxidizing bactericide to be added next can be reduced. In particular, by using it in combination with high-alkalinity PAC, the pH adjustment of the raw water can be omitted. Therefore, the amount of added agents such as pH adjusters, reducing agents, and bactericides can be significantly reduced; their operating load. In particular, when high-alkalinity PAC is used in the previous treatment and pH adjustment is not performed, if sodium pyrosulfite is used, in which the amount of reducing agent remaining does not change even if pH changes, in other words, the amount of residual chlorine does not change, it is possible to avoid the influence of pH changes, such as the clogging of the reverse osmosis membrane by bacteria due to insufficient bactericide, and the deterioration of the reverse osmosis membrane due to insufficient reducing agent. In addition, the amount of residual reducing agent can be ignored, so in the method of monitoring the residual chlorine amount and adding the optimal amount thereto, it is also easy to set the optimal amount of addition. It should be noted that the reducing agent contains, in addition to the active ingredient, for example, water as a solvent, and may also contain a stabilizer.

[0034] In contrast, when sodium sulfite (Na2SO3) and sodium bisulfite (NaHSO3) are used as reducing agents, the residual amount of reducing agent is large in all pH regions, and the residual amount varies depending on the pH value. The reason may not be clear, but sodium sulfite (Na2SO3) and sodium bisulfite (NaHSO3) are in equilibrium with each other. If sodium sulfite (Na2SO3) or sodium bisulfite (NaHSO3) is added to raw water, the equilibrium shift reaction proceeds due to pH changes. At the same time, the redox reaction of sodium sulfite (Na2SO3) and sodium bisulfite (NaHSO3) with free chlorine occurs. Therefore, it can be considered that the redox reaction rate is slower than the equilibrium shift reaction according to the pH of the raw water, so the amount of sodium sulfite (Na2SO3) and sodium bisulfite (NaHSO3) added becomes more. Moreover, the increase in the amount of addition is sometimes affected by the amount of oxidant, the scale of the device, the difference in the stirring speed after adding the reducing agent, etc., so even if the pH of the raw water is the same, it may not be a constant amount, so it is difficult to set an appropriate amount of addition.

[0035] In the manufacturing device 1 of the present embodiment, the amount of reducing agent added also depends on the free chlorine concentration of the raw water, but is preferably 0.1 mg / L to 5 mg / L in terms of the amount of the effective ingredient (sodium pyrosulfite). In particular, when the free chlorine concentration is about 0.2 mg / L in terms of Cl2, the amount of the effective ingredient (sodium pyrosulfite) can be set to 0.2 mg / L to 0.4 mg / L, and the amount of residual reducing agent can be suppressed to, for example, below 0.06 mg / L. In addition, the amount of reducing agent added can also be determined as described below. For example, an ORP meter (oxidation-reduction potentiometer), a residual chlorine meter, a SO2 meter, etc. can be used to monitor the free chlorine concentration, and the amount of reducing agent added can be adjusted according to the monitored amount. In addition, the amount of reducing agent remaining after adding the reducing agent can also be monitored, and the amount of reducing agent added can be feedback controlled according to the monitored value. The reducing agent amount can be quantitatively monitored by, for example, obtaining a portion of raw water to which the reducing agent is added as sample water, comparing the dissolved oxygen concentrations obtained by irradiating the raw water and the sample water with ultraviolet light, and determining the reducing agent amount in the sample water.

[0036] Next, as needed, the bactericide supply device 18 adds an oxidizing bactericide to the second treated water. The bactericide supply device 18 includes, for example, a liquid medicine tank storing the oxidizing bactericide and an injection pump for adding the oxidizing bactericide in the liquid medicine tank to the raw water delivery pipe 13. The injection pump measures a predetermined amount of the oxidizing bactericide in the liquid medicine tank and adds it to the raw water delivery pipe 13.

[0037] As oxidizing bactericide, oxidizing bactericides other than free chlorine can be used, for example, oxidizing bactericides such as amine compounds and aminosulfonic acid compounds can be listed. It is also possible to include halogens bonded to aminosulfonic acid compounds such as aminosulfonyl chloride and chloroaminosulfonic acid. In addition, it is also possible to include isothiazolin compounds such as 5-chloro-2-methyl-4-isothiazoline-3-one and 2-methyl-4-isothiazoline-3-one (MIT), bromic acid compounds such as sodium hypobromite, and 2,2-dibromo-3-nitrilopropionamide (DBNPA). In oxidizing bactericide, it is also possible to include components of stabilized halogen forms and aminosulfonic acid compounds of residual amount. Thus, in addition to using stabilized hypochlorous acid and stabilized hypobromous acid, stabilized halogen acid salts can also be used as bactericides. As the oxidizing bactericide, a commercially available product may be used, and examples of the commercially available product include Kuriverter IK110 manufactured by Kurita Industries, ORPERSION E266 series manufactured by ORGANO, KATHON WT manufactured by Dow Chemical, and Stabrex manufactured by Nalco.

[0038] The amount of bactericide added is usually preferably an amount for inhibiting bacterial growth, and the MIC (minimuminhibitory concentration) of the bacteria contained in the raw water is preferably confirmed in advance, and the amount to reach the MIC to about 5 times the MIC is added. In particular, in the present embodiment, the residual amount of the reducing agent is small, so the amount of oxidizing bactericide lost by the reducing agent is small, so it is sufficient to use an amount to reach the MIC.

[0039] Next, the second treated water to which the bactericide is added is supplied to the reverse osmosis membrane device 14 via the delivery pipe 13 and subjected to reverse osmosis membrane treatment. Thus, permeate water of the reverse osmosis membrane device 14 is obtained. In order to suppress the decrease in the permeate flux in the reverse osmosis membrane device 14, the water supply pressure to the reverse osmosis membrane device 14 is preferably 0.5 MPa to 3 MPa, and the water recovery rate in the reverse osmosis membrane device 14 is preferably 75% to 95%. Immediately before being supplied to the reverse osmosis membrane device 14, an antiscalant may be appropriately added to the second treated water and then supplied to the reverse osmosis membrane device 14.

[0040] As the reverse osmosis membrane device 14, any type of reverse osmosis membrane device in the ultra-low pressure type, ultra-low pressure type, low pressure type, medium pressure type, and high pressure type can be used. As the reverse osmosis membrane possessed by the reverse osmosis membrane device 14, a spiral reverse osmosis membrane with aromatic polyamide as the constituent material is preferred. In addition, as the reverse osmosis membrane device 14, there are positive charge membranes with positive charges on the surface of the reverse osmosis membrane, negative charge membranes with negative charges on the surface, and non-charged membranes with no charges on the surface, among which the negative charge membrane is not prone to blockage caused by flocculants of the reverse osmosis membrane, so it is preferred. As the reverse osmosis membrane device 14, an ultra-low pressure or low pressure type negative charge membrane is preferred. As a reverse osmosis membrane device with an ultra-low pressure or low pressure type negative charge membrane, a commercially available product can be used, for example, "ES20" manufactured by Nitto Denko Corporation, "SU series", "TM series", "TBW series" manufactured by Toray Industries, Ltd., and "BW series" manufactured by Dow Corporation can be used.

[0041] The permeate water of the reverse osmosis membrane device 14 is sent to the rear stage via the transport pipe 15 on the permeate side of the reverse osmosis membrane device 14. The concentrated water of the reverse osmosis membrane device 14 can be discharged to the outside of the system of the manufacturing device 1 via the discharge pipe 16, or returned to the front stage of the reverse osmosis membrane device 14 for reprocessing. The water quality of the permeate water of the reverse osmosis membrane device 14 thus obtained is, for example, turbidity of 0.01NTU to 0.2NTU, aluminum concentration of 0mg / L to 0.002mg / L, pH of 5.9 to 6.5, and conductivity of 30μS / cm to 100μS / cm.

[0042] Next, another embodiment of the present invention will be described. Figure 3The production device 3 used in the method for producing pure water of this embodiment is schematically shown. The production device 3 is similar to the present invention in that it includes a filter 31 between the polyaluminium chloride supply device 12 and the reducing agent supply device 17 on the path of the raw water delivery pipe 13. Figure 1 The manufacturing apparatus 1 shown is different, but the other structures are the same. In this embodiment, the detailed description of the same structure and function as the manufacturing method using the manufacturing apparatus 1 is omitted.

[0043] Used Figure 3 The method for producing pure water in the embodiment of the production device 3 shown is as follows. First, raw water is supplied from the raw water supply device 11 to the raw water delivery pipe 13. Then, PAC is added to the raw water delivery pipe 13 supplied with raw water by the polyaluminium chloride supply device 12. The preferred embodiment of the PAC used here is Figure 1 The manufacturing method of the manufacturing device 1 shown is the same.

[0044] When high alkalinity PAC is used, raw water and high alkalinity PAC are supplied into the raw water delivery pipe 13, and suspended matter in the raw water interacts with high alkalinity PAC to form microflocs. By passing through the microflocs, the adhesion of residual aluminum to the membrane of the reverse osmosis membrane device 14 can be significantly reduced, and the performance of the reverse osmosis membrane device can be maintained for a long time.

[0045] The first treated water in the raw water delivery pipe 13 is supplied to the filter 31. At this time, by providing a water supply pump in the raw water delivery pipe 13, the first treated water can be supplied to the filter 31 by the water supply pump. In this embodiment, a mixing tank is not used, so the manufacturing device becomes compact, which has the advantage of being easy to be installed in a semiconductor manufacturing plant, etc. It should be noted that if a pipeline mixer or the like is provided in the raw water delivery pipe 13 after the PAC is supplied in order to promote mixing, clogging of the equipment in the subsequent stage is further suppressed.

[0046] The filter unit 31 includes one or more filter devices selected from a sand filter device, a multi-media filter (MMF) filter device, an ultrafiltration device, and a microfiltration (MF) device, and performs a filtering treatment on the first treated water. Thus, microflocculates, which mainly contain suspended matter in the water, are removed. The treated water of the filter unit 31 is sent to the rear section through a pipe.

[0047] The sand filter device has, for example, supporting gravel or sand (filter sand) as filter material. The multi-media filter (MMF) filtration device includes, for example, a filter material having a three-layer structure in which anthracite, sand, and garnet are stacked from bottom to top in order of particle size. The ultrafiltration (UF) device includes an ultrafiltration membrane with a nominal pore size of 0.001 to 0.1 μm as a filter material, and may be either a full-flow filtration method or a cross-flow filtration method. The ultrafiltration (UF) device is preferably an external pressure ultrafiltration device using a hollow fiber membrane. The microfiltration (MF) device includes, for example, a microfiltration membrane having a nominal pore size of 0.1 to 5 μm, and is capable of full volume filtration.

[0048] The filter section 31 may have one of the above-mentioned filter devices selected from the group consisting of a sand filter device, a multi-media filter (MMF) filter device, a microfiltration (MF) device, and an ultrafiltration (UF) device, or a combination of two or more, depending on the quality of the raw water. In the case of a combination of two or more, it is preferred to configure a sand filter device and a multi-media filter (MMF) filter device on the upstream side, and an ultrafiltration device on the downstream side. The filter section 31 is more preferably equipped with an ultrafiltration device, and it is further preferred to only have an ultrafiltration device. By providing the filter section 31, suspended matter in the first treated water can be removed with high precision, thereby reducing the load of the reverse osmosis membrane device 14 in the rear section, and thus high-quality permeate water can be obtained for a long time.

[0049] exist Figure 3 In the manufacturing device 3 shown, the filter unit 31 is an independent filter unit having an independent filter device. As independent filter devices, a cartridge filter device and a module filter device can be listed. The cartridge filter device is, for example, constructed as follows: a cartridge containing filter material in a shell, a pipe connected to a water inlet and a drain outlet opened in the shell, and water is passed into the cartridge through the opening. The cartridge filter device has the following advantages: when the filter material deteriorates, only the cartridge can be replaced. The module filter device is constructed as follows: the filter material is arranged inside the shell, and the module is connected to the pipe, thereby passing water to the filter material. In the module filter device, there are the following advantages: when the filter material deteriorates, it can be replaced according to each module, and the deteriorated filter material can be cleaned and regenerated according to each module. According to the independent filter unit 31, the outflow of nano-floc to the downstream side is small, so it is effective in preventing the clogging of the reverse osmosis membrane device 14. It should be noted that nano-floc is a flocculent finer than micro-floc, which is easy to aggravate the clogging of the reverse osmosis membrane. In particular, when the method of this embodiment is used to manufacture ultrapure water for manufacturing semiconductors, etc., by using an independent filter unit 31, a plurality of independent filter units 31 are pre-arranged in parallel, and regeneration such as backwashing and module replacement are performed one by one among the plurality of units, and the operation is continued by other devices (so-called carousel operation), thereby continuously manufacturing ultrapure water without stopping the device.

[0050] The water quality of the treated water of the filter unit 31 thus obtained is, for example, turbidity of 0.01 NTU to 0.4 NTU, aluminum concentration of 0.01 mg / L to 0.04 mg / L, pH of 7.2 to 8.3, and conductivity of 140 μS / cm to 270 μS / cm. When high-alkalinity PAC is used, homogeneous microflocculates can be stably formed regardless of the pH value of the raw water to which the high-alkalinity PAC is added, so it is not necessary to add a pH adjuster to the mixing tank 23, and the amount of chemicals used can be reduced. Therefore, although the pH of the treated water of the filter unit 31 sometimes fluctuates, the aluminum concentration remains low and stable.

[0051] Figure 4 The schematic diagram shows a pure water production device 4 having a mixing tank 23 for adding PAC to raw water and a filter unit 31. The production device 4 has a mixing tank 23 and a delivery pipe 131 for supplying water in the mixing tank 23 to the rear stage on the path of the raw water delivery pipe 13, and the filter unit 31, the reducing agent supply device 17, and the disinfectant supply device 18 are sequentially arranged on the path of the delivery pipe 131. Figure 3 The manufacturing apparatus 3 shown is different, but the other configurations are the same. In this embodiment, detailed description of the same configurations and functions as those of the manufacturing method using the manufacturing apparatus 3 is omitted.

[0052] In the production device 4, raw water is supplied from the raw water supply device 11 to the mixing tank 23, and PAC is supplied from the polyaluminium chloride supply device 12 to the mixing tank 23. When low alkalinity PAC is used, the pH adjustment device supplies acid and alkali to the mixing tank 23. Thus, first treated water is generated.

[0053] When high alkalinity PAC is used, it is not necessary to add acid and alkali using a pH adjustment device. When high alkalinity PAC is used, suspended matter in raw water interacts with high alkalinity PAC in the mixing tank 23, thereby forming microflocs. In particular, by using the mixing tank 23, the formation of microflocs based on high alkalinity PAC is fully performed, thereby further suppressing the clogging of the equipment in the subsequent stage. In this case, the order of supplying to the mixing tank 23 may be either raw water or high alkalinity PAC first, or both, and it is preferred to add high alkalinity PAC to the mixing tank 23 supplied with raw water.

[0054] Figure 4 The manufacturing apparatus 4 shown has an independent type filtering unit 31 which is separate and independent from the mixing tank 23 at the rear stage of the mixing tank 23. The configuration of the independent type filtering unit 31 is the same as that of the manufacturing apparatus 3 described above.

[0055] In addition, as the filter unit 31, an immersion type filter device configured for tank immersion can be used. The immersion type filter device configured for tank immersion is immersed in the bottom of the mixing tank 23, which has the following advantages: the first treated water added with PAC can be filtered directly by the filter device without using piping. As the immersion type filter device, an ultrafiltration device and an MMF type filter device are preferred. In the manufacturing device 4 of this embodiment, in particular, when using high-alkalinity PAC, by forming microflocs in water as the main body, it is possible to directly perform filtering treatment without precipitation removal using a coagulation sedimentation tank. Therefore, the filter unit 31 can be immersed in the mixing tank 23 and integrated, which can simplify the overall structure of the device.

[0056] In the filtration unit 31, when a plurality of filtration devices are used, only the immersed type or only the independent type may be used, or both the immersed type and the independent type may be used. In this embodiment, it is preferred to use only the independent type filtration device, and it is more preferred to use the independent type ultrafiltration device. As the ultrafiltration membranes possessed by independent ultrafiltration devices, there are hollow fiber membranes, spiral membranes, and flat membranes made of materials such as cellulose acetate, aromatic polyamide, polyvinyl alcohol, polysulfone, and polyvinylidene fluoride. Among them, hollow fiber membranes made of fluorine-based materials such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) are preferred. As the filtration membrane provided in the immersion type ultrafiltration device, a flat membrane made of ceramic or a fluorine-based material such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) is preferable.

[0057] By utilizing Figure 3 or Figure 4 The filter unit 31 filters the first treated water, and the micro-flocs and coarse floccules including suspended matter in the water are removed. Next, the reducing agent supply device 17 adds a reducing agent to the treated water of the filter unit 31. Thus, the second treated water is generated. Furthermore, as needed, the bactericide supply device 18 adds an oxidizing bactericide to the second treated water, and then supplies the second treated water with the oxidizing bactericide added to the reverse osmosis membrane device 14. The preferred embodiment of adding a reducing agent and adding an oxidizing bactericide is the same as that of the above-mentioned manufacturing device 1 ( Figure 1 ) and manufacturing device 2 ( Figure 2 )same.

[0058] Next, refer to Figure 5 A pure water production system 5 according to an embodiment using the above-described production apparatus 1 will be described. Figure 5 1 is a block diagram schematically showing the structure of an ultrapure water production system 5 using the production apparatus 1. Figure 5 In the above description, the production apparatus 1 can be changed to any one of the production apparatuses 2 to 4 .

[0059] like Figure 5 As shown, the ultrapure water production system 5 sequentially includes a pretreatment system 50, a primary pure water system (pure water production system) 51, and a secondary pure water system (subsystem) 52. The secondary pure water system 52 is connected to a point of use (POU) 53 via piping, so that the ultrapure water produced by the ultrapure water production system 5 is supplied to the POU 53.

[0060] The pretreatment system 50 includes the production apparatus 1 of the above-described embodiment and, if necessary, a prefilter, a heat exchanger for temperature control, and the like.

[0061] The ultrapure water production system 5 includes a tank TK1 at the downstream of the pretreatment system 50 . The treated water pretreated by the pretreatment system 50 is introduced into the tank TK1 and temporarily stored, and then supplied to the primary pure water system 51 .

[0062] The primary pure water system 51 removes organic matter, ion components, and dissolved gases from pre-treated water to produce primary pure water. The primary pure water system 51 includes an ultraviolet oxidizing device (TOC-UV) 513 and an ion exchange device 514 in this order.

[0063] The ultraviolet oxidizing device 513 has, for example, an ultraviolet lamp that radiates ultraviolet rays with a wavelength of about 185 nm and ultraviolet rays with a wavelength of about 254 nm. By irradiating the water to be treated with ultraviolet rays from the ultraviolet lamp, the total organic carbon component (TOC) in the water to be treated is oxidized and decomposed. The ultraviolet rays radiated by the ultraviolet oxidizing device 513 decompose the water to generate OH radicals, and the organic matter in the water to be treated is oxidized and decomposed into organic acids by the OH radicals. The amount of ultraviolet irradiation in the ultraviolet oxidizing device 513 of the primary pure water system can be appropriately changed according to the water quality of the water to be treated.

[0064] The ion exchange device 514 is one or more of an ion exchange resin device and an electrodeionization device. As the ion exchange resin device, one or more selected from a cation exchange resin device, an anion exchange resin device, a mixed bed ion exchange resin device and a multiple bed ion exchange resin device can be used in combination according to the required water quality. The cation exchange resin used in the cation exchange resin device can be a strongly acidic cation exchange resin or a weakly acidic cation exchange resin. The anion exchange resin used in the anion exchange resin device can be a strongly basic anion exchange resin or a weakly basic anion exchange resin. As the ion exchange resin, a boron adsorbing ion exchange resin can also be used.

[0065] The primary pure water obtained by the primary pure water system 51 has, for example, a resistivity of 17 MΩ·cm or more and a TOC concentration of 10 μgC / L or less.

[0066] The ultrapure water production system 5 is provided with a primary pure water tank TK2 for storing primary pure water and a secondary pure water system 52 in the subsequent stage of the primary pure water system 51. The primary pure water produced by the primary pure water system is temporarily stored in the primary pure water tank TK2 and then sent to the secondary pure water system 52. The secondary pure water system 52 is provided with an ultraviolet oxidizing device (TOC-UV) 521, an ion exchange device (Polisher) 522 for non-regenerative ultrapure water production, a membrane degassing device (MDG) 523, and an ultrafiltration device (UF) 524.

[0067] The structure of the ultraviolet oxidation device 521 in the secondary pure water system 52 is the same as that of the ultraviolet oxidation device 513 in the primary pure water system 51. The non-regenerative ultrapure water production ion exchange device 522 is a mixed bed ion exchange resin device in which a strongly acidic cation exchange resin and a strongly basic anion exchange resin are mixed and filled in a container such as a gas cylinder. The non-regenerative ultrapure water production ion exchange device 522 adsorbs and removes ion components generated by decomposing organic matter by the ultraviolet oxidation device 521.

[0068] The membrane degassing device 523 removes dissolved gas via a degassing membrane. The membrane degassing device 523 removes trace dissolved oxygen in the primary pure water, reducing the dissolved oxygen concentration to, for example, about 1 μg / L or less. The ultrafiltration device 524 performs filtration processing using an ultrafiltration membrane to remove trace elutions and particulate components from the ion exchange resin on the upstream side, for example, reducing the number of particles larger than 0.05 μm to about 250 Pcs. / L or less.

[0069] In this way, the secondary pure water system 52 processes the primary pure water to produce ultrapure water with higher purity. As for the quality of the ultrapure water, for example, the total organic carbon (TOC) concentration is less than 1 μgC / L, the resistivity is more than 18 MΩ·cm, and the boron concentration is less than 0.1 ppb (μg / L). The ultrapure water produced in the secondary pure water system is supplied to the use point 53.

[0070] It should be noted that, in each of the above-mentioned embodiments, the water quality of raw water and treated water can be measured by the following methods or devices, respectively. Turbidity: A measure of light scattering. Aluminum concentration: ICP luminescence analysis. pH: electrode method. Electrical conductivity: Electrical conductivity meter (HE-960CW manufactured by Horiba, Ltd.). Total organic carbon (TOC) concentration: TOC meter (except ultrapure water: Sievers M9e manufactured by SUEZ Corporation). Example

[0071] Next, examples will be described. The present invention is not limited to the following examples.

[0072] Figure 6 The pure water production apparatus 6 used in the present example and the comparative example is schematically shown. Figure 6 The manufacturing device 6 shown in the figure includes: a raw water supply device 61 for supplying raw water; a polyaluminium chloride supply device 62 for supplying PAC; and a mixing tank 63 for supplying raw water and PAC inside. The manufacturing device 6 also includes an ultrafiltration device 65, a reducing agent supply device 67, a bactericide supply device 68, and a reverse osmosis membrane device 64 in the path on the downstream side of the mixing tank 63.

[0073] The specifications of each device used in the Examples and Experimental Examples are as follows. Mixing tank 63: capacity 1m 3 . Ultrafiltration device 65: Purear GL manufactured by Kuraray Corporation (PVDF membrane, nominal pore size 0.02 μm). Reverse osmosis membrane device 64: TM710 manufactured by Toray Industries, Inc. (low-pressure type, load-electric membrane). Water recovery rate 85%, operating pressure 12kgf / cm 2 . Determination of aluminum concentration: high frequency inductively coupled plasma (ICP) luminescence analysis. Turbidity measurement: Turbidimeter (Hach2100P, manufactured by TOADKK Co., Ltd.). pH measurement: water quality meter (Horiba 9630-10D, manufactured by Horiba Corporation). Residual chlorine concentration or total chlorine concentration: AQ-201 (manufactured by SIBATA). Sulfite ion (SO3 2- ) Concentration (reducing agent amount): MD600 (manufactured by LOVIBOND). Free chlorine concentration: AQ-201 (manufactured by SIBATA). The quality of the raw water (lake water): turbidity 4 NTU, pH = 7.2, conductivity 250 μS / cm, TOC 4 mg / L. It should be noted that the pH fluctuated between 6.7 and 7.8 during the water flow period.

[0074] (Example 1) Hypochlorous acid was added to the raw water so that the free chlorine concentration was 0.2 mg / L in terms of Cl2, and the raw water was supplied to the mixing tank 63. Then, an aqueous solution of hydroxyaluminum chloride (Al2Cl(OH)5) (a trial product of Nomura Microscience Co., Ltd., with an alkalinity of 83.33%) was added as a high-alkalinity PAC so that the aluminum concentration in the raw water was 1.2 mg / L in terms of Al2O3, and the raw water was stirred. After stirring, the raw water was sampled and 80 ml of the raw water was passed through a membrane with a nominal pore size of 0.2 μm (size 2.0 μm). ) and observed the particles captured by the membrane. As a result, particles of about 1 to 10 μm were observed. The elemental composition of the particles was confirmed by energy dispersive X-ray fluorescence spectroscopy (EDX), and the results showed that they contained Al. In addition, for the membrane with a nominal pore size of 0.45 μm (large ) When the same amount of water was passed, there was almost no pressure difference. Based on the above results, it was confirmed that microflocculation was formed in this example.

[0075] The treated water in the mixing tank 63 is passed through the ultrafiltration device 65, filtered, and then sent to the back stage through the pipe. In this process, 0.2 mg / L of sodium pyrosulfite is added as a reducing agent, and then 0.3 mg / L of chloroaminosulfonic acid (NOMULITE (prototype), manufactured by Nomura Microscience Co., Ltd.) is added as an oxidizing bactericide. Then, the treated water is supplied to the reverse osmosis membrane device 64 for reverse osmosis membrane treatment. It should be noted that the amount of sodium pyrosulfite added is set to the minimum amount (chemical equivalent) required for the next reaction to occur completely. Na2S2O5+H2O+2NaOCl→2HCl+2Na2SO4

[0076] (Example 2) In Example 1, except that high basicity PAC (basicity 76%) produced by the method described in Japanese Patent No. 4104773 was used as high basicity PAC, the treatment was continued in the same manner as in Example 1 using the ultrafiltration device 65 and the reverse osmosis membrane device 64 in this order. In Example 2, formation of microflocs was also confirmed.

[0077] (Example 3) In Example 1, except that 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (MIT) were added in a total of 0.05 mg / L as oxidizing bactericides, the treatment was continued in the same manner as in Example 1 using the ultrafiltration device 65 and the reverse osmosis membrane device 64 in this order. In Example 3, the formation of microflocs was also confirmed.

[0078] (Example 4) Acid or alkali was added to the raw water to maintain the pH at 7.2 to eliminate pH fluctuations. In addition, low-alkalinity PAC (trade name PAC250A, manufacturer: Taki Chemical Co., Ltd., alkalinity 50%) was used as PAC so that the aluminum concentration in the raw water was 0.3 to 0.4 mg / L in terms of Al2O3. In the same manner as in Example 1, the treatment was continued in sequence using the ultrafiltration device 65 and the reverse osmosis membrane device 64. In Example 4, the raw water after adding the low-alkalinity PAC and stirring was sampled, and 80 ml of the raw water was passed through a membrane with a nominal pore size of 0.2 μm (larger than 10 μm). ) and observed the particles captured by the membrane. The results showed that the particles were about 1 to 10 μm in size. The elemental composition of the particles was confirmed by EDX, and the results showed that they contained Al. When the same amount of water was passed, a pressure difference was generated suddenly. From the above results, it was confirmed that, although fine flocs were formed, coarse aggregates with a size of 0.45 μm or more were also formed.

[0079] (Comparative Example 1) In Example 1, except that low-alkalinity PAC (trade name PAC250A, manufacturer: Taki Chemical Co., Ltd., alkalinity 50%) was used as PAC so that the aluminum concentration in the raw water was 0.3 to 0.4 mg / L in terms of Al2O3, the treatment was continued in the same manner as in Example 1 using the ultrafiltration device 65 and the reverse osmosis membrane device 64 in sequence. In Comparative Example 1, the formation state of flocs was the same as in Example 4.

[0080] (Comparative Example 2) In Comparative Example 1, except that 0.05 mg / L of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one (MIT) were added as oxidizing bactericides, the ultrafiltration device 65 and the reverse osmosis membrane device 64 were used in the same manner as in Comparative Example 1. The formation state of flocs was the same as in Comparative Example 1.

[0081] (Comparative Example 3) In Example 1, except that sodium sulfite was used as a reducing agent, the treatment was continued in the same manner as in Example 1 using the ultrafiltration device 65 and the reverse osmosis membrane device 64 in sequence. In Comparative Example 3, the state of formation of microflocs was the same as in Example 1. It should be noted that the amount of sodium sulfite added was set to the minimum amount (chemical equivalent) required for the next reaction to completely occur. NaOCl+Na2SO3→NaCl+Na2SO4

[0082] (Comparative Example 4) In Example 1, except that sodium bisulfite was used as a reducing agent, the treatment was continued in the same manner as in Example 1 using the ultrafiltration device 65 and the reverse osmosis membrane device 64 in sequence. In Comparative Example 3, the state of formation of microflocs was the same as in Example 1. It should be noted that the amount of sodium bisulfite added was set to the minimum amount (chemical equivalent) required for the next reaction to completely occur. 2NaHSO3+3NaClO→3NaCl+H2O+2Na2SO4

[0083] The types and alkalinity of PAC used in Examples 1 to Comparative Examples 4, the types and addition amounts of reducing agents, the types of oxidizing bactericides, the aluminum concentration, turbidity (NTU) and residual reducing agent concentration in the treated water of the ultrafiltration device 65 are shown in Table 1. In Table 1, the amount of reducing agent is expressed as the amount of effective ingredient, and the residual amount of reducing agent is expressed as sulfite ions (SO3 2- It should be noted that in Table 1, the mixture of 5-chloro-2-methyl-4-isothiazoline-3-one and 2-methyl-4-isothiazoline-3-one (MIT) is represented as "fungicide b".

[0084]

Table 1

[0085] Comparison of Example 1 with Comparative Examples 3 and 4 shows that the permeate flux (flow rate) increases in Comparative Examples 3 and 4. This is considered to be because sodium sulfite (Na2SO3) is used in Comparative Example 3 and sodium bisulfite (NaHSO3) is used in Comparative Example 4, and therefore the amount of the reducing agent is insufficient in the reaction equivalent with the oxidizing agent (free chlorine), and therefore the deterioration of the reverse osmosis membrane provided in the reverse osmosis membrane device 64 is accelerated in the short period of 3 months, and thus the permeate flux increases.

[0086] (Experimental Examples 1 to 3) The relationship between the type of reducing agent and the residual amount when the pH of raw water was changed was investigated. A predetermined amount of raw water with a turbidity of 4 was collected in a beaker, and a pH adjuster (NaOH or H2SO4) was added thereto to adjust the pH to a predetermined value of pH = 6 to 9. Sodium hypochlorite (NaClO) was added to each pH-adjusted sample so that the free chlorine concentration was 2 mg / L in terms of Cl2. Next, a predetermined amount (0 to 20 mg / L) of the reducing agent shown below was added until the free chlorine concentration disappeared. 2- The concentration was measured. The amount of reducing agent remaining when free chlorine disappears is calculated from the difference between the amount of reducing agent added and the amount of reducing agent consumed according to the reaction formula. Figure 7 .

[0087] Experimental Example 1: Sodium metabisulfite (Na2S2O5). Experimental Example 2: Sodium sulfite (Na2SO3). Experimental Example 3: Sodium bisulfite (NaHSO3).

[0088] According to Experimental Examples 1 to 3, when sodium sulfite (Na2SO3) is used as a reducing agent and sodium bisulfite (NaHSO3) is used as a reducing agent, the reducing agent remains when added until free chlorine disappears, and the residual amount varies depending on the pH. In contrast, when sodium pyrosulfite (Na2S2O5) is used, the residual amount of the reducing agent is less than sodium sulfite and sodium bisulfite, and the pH dependence of the residual amount is also low.

[0089] According to the experimental examples, embodiments and comparative examples described above, according to the manufacturing device and manufacturing method of pure water of the embodiment, since sodium pyrosulfite (Na2S2O5) is used as a reducing agent, the residual amount of the reducing agent is less than that of sodium sulfite and sodium bisulfite, and the pH dependence of the residual amount is also low. Therefore, in the case of reverse osmosis membrane treatment of raw water containing chlorine, the reagent can be added efficiently and its addition amount can be reduced. As a result, high-purity pure water and ultrapure water can be manufactured efficiently and for a long time, so the manufacturing device and manufacturing method of pure water of the embodiment are suitable for mass production of pure water or ultrapure water.

Claims

1. A method for producing pure water, comprising: A step of adding polyaluminium chloride to raw water containing free chlorine to obtain first treated water; A step of adding a reducing agent having sodium pyrosulfite as an effective ingredient to the first treated water to obtain a second treated water; and A reverse osmosis membrane step of subjecting the second treated water to reverse osmosis membrane treatment.

2. The manufacturing method according to claim 1, wherein: High-alkalinity polyaluminium chloride is added to the raw water, thereby obtaining first treated water containing microflocs.

3. The manufacturing method according to claim 1 or 2, wherein: The turbidity of the raw water is greater than or equal to 1 NTU and less than or equal to 100 NTU.

4. The manufacturing method according to claim 1 or 2, wherein: The basicity of the polyaluminium chloride is greater than 75%.

5. The manufacturing method according to claim 1 or 2, wherein: The polyaluminium chloride comprises hydroxyaluminium chloride, The amount of the hydroxyaluminum chloride added is 0.25 mg / L or more and 5 mg / L or less relative to the raw water in terms of the concentration of aluminum oxide Al 2 O 3 .

6. The manufacturing method according to claim 1 or 2, wherein: include: A filtration step, filtering the first treated water by one or more selected from sand filtration, multi-media filter MMF filtration, microfiltration MF device and ultrafiltration, The reducing agent is added to the treated water obtained in the filtration step.

7. The manufacturing method according to claim 1 or 2, wherein: The free chlorine concentration in the raw water is 0.1 mg / L or more and 2 mg / L or less in terms of Cl2, and the amount of the reducing agent added is 0.1 mg / L or more and 5.0 mg / L or less in terms of the amount of sodium pyrosulfite.

8. The manufacturing method according to claim 1 or 2, wherein: The turbidity of permeated water of the reverse osmosis membrane device is 0.01 to 0.4, and the aluminum concentration is 0.01 to 0.04 mg / L.

9. A method for producing pure water, comprising: The process for producing pure water comprises: a process of adding polyaluminium chloride to raw water containing free chlorine to obtain first treated water; a process of adding a reducing agent containing sodium pyrosulfite as an effective ingredient to the first treated water to obtain second treated water; and a reverse osmosis membrane process of performing reverse osmosis membrane treatment on the second treated water; UV oxidation process; and Ion exchange process.

10. A device for producing pure water, comprising: A raw water supply device for supplying raw water containing free chlorine; A polyaluminium chloride supply device for adding polyaluminium chloride to raw water; a reducing agent supplying device for adding a reducing agent having sodium pyrosulfite as an effective ingredient to first treated water generated by adding polyaluminium chloride to raw water; and The reverse osmosis membrane device performs reverse osmosis membrane treatment on the second treated water generated by adding the reducing agent.

11. The manufacturing device according to claim 10, wherein: The turbidity of the raw water is greater than or equal to 1 NTU and less than or equal to 100 NTU.

12. The manufacturing device according to claim 10 or 11, wherein: The basicity of the high-basicity polyaluminium chloride is greater than 75%.

13. The manufacturing device according to claim 10 or 11, wherein: The polyaluminium chloride comprises hydroxyaluminium chloride, The polyaluminium chloride supply device supplies aluminium hydroxy chloride in an amount of 0.25 mg / L or more and 5 mg / L or less in terms of the concentration of aluminium oxide Al 2 O 3 relative to the raw water.

14. The manufacturing device according to claim 10 or 11, wherein: Between the polyaluminium chloride supply device and the reducing agent supply device, there is one or more selected from a sand filter device, a multi-media filter MMF filter device, a microfiltration MF device and an ultrafiltration device.

15. A pure water production system, comprising: The device for producing pure water as claimed in claim 14; UV oxidation devices; and Ion exchange device.

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